WASHINGTON (CNN) -- Attorneys for John Walker Lindh, who pleaded guilty in July 2002 to a charge of aiding the Taliban, are asking President Bush to reduce his 20-year prison sentence.

The attorneys argue the cases of Lindh and Yaser Hamdi, both captured by the U.S.-allied Northern Alliance after fighting with the Taliban, are comparable in many ways and the two men should receive equal punishment.

While Hamdi was designated an "enemy combatant" and held by the U.S. military without ever facing charges, Lindh was brought back to the United States and put into the criminal justice system.

Lindh originally also faced charges of conspiracy to murder U.S. nationals and providing material support to terrorists, but they were dropped as part of the plea deal.

U.S. officials have said the government has its reasons for decisions about how to deal with different detainees.

While Lindh's attorneys argue neither he nor Hamdi fought against American troops, the government has alleged both were captured while fighting alongside Taliban forces after the U.S. invasion of Afghanistan.

It is "basically unfair" to have Lindh serve the remainder of his 20-year sentence, his attorney, James Brosnahan, said during a news conference in San Francisco. He argued that his client got a tougher plea bargain sentence than other defendants who have reached deals with the Justice Department.

He said he is not asking for a specific time reduction, but indicated a three-year sentence, the same general amount of time Hamdi has been held, would be appropriate.

"I don't consider it a long shot," Brosnahan said of the request, which is going to the White House as well as the Justice Department.

There was no immediate comment from the White House or Justice Department.

Attorneys for Hamdi and the U.S. government last week announced an agreement under which he would be released from U.S. custody and sent back to his native Saudi Arabia without ever facing any formal charges. (Full story)

Hamdi, who has to agree to give up his U.S. citizenship and has to abide by a set of travel restrictions, is expected to leave the United States as soon as this week.

Hamdi was born in Louisiana in 1980, but his family moved back to Saudi Arabia while he was a youngster